Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do you find

  1. Mar 27, 2004 #1
    How do you find....

    Im wondering whether how you find the speed of
    a) space shuttle

    and

    b) submarines?
    Any answer will be appreciated :smile:
     
  2. jcsd
  3. Mar 27, 2004 #2

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The space shuttle must have a large enough tangential velocity to keep it in orbit. The velocity of a satellite in a circular orbit at a known altitude can be easily calculated:

    http://hyperphysics.phy-astr.gsu.edu/hbase/orbv3.html

    The velocity of a submarine, however, is up for grabs. The submarine could, of course, just stop and sit still.

    The maximum speed that a submarine can reach will be the point where its engine output (in horsepower, for example) equals its losses due to hydrodynamic friction (drag). This assumes, of course, that the submarine's hull is capable of handling that kind of drag and so on. If you know the frontal area and drag coefficient of the sub, plus its maximum engine output, the top speed is also easy to calculate. You could probably look up the drag coefficient for a hemispherical front-end, which I believe most subs have. These kinds of things are difficult to calculate accurately without a lot of very specific, detailed measurements.

    http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html#c2

    - Warren
     
  4. Mar 27, 2004 #3
    ok. I see...
    If such speed is attainable, so how does technology achieve such speed? :confused:
     
  5. Mar 28, 2004 #4

    LURCH

    User Avatar
    Science Advisor

    It's also important to bear in mind that speed is always relative. This may not be terribly important for the shuttle, but it is a significant factor for the sub. Because a submarine travels through a fluid medium, much like aircraft, it has two important speeds to be calculated; water speed and ground speed. For example, if a submarine is traveling through a part of the ocean in which there is a prevailing current that moves eastward at approximately seven knots, and the sub shows a water speed of 30 knots with the heading of East, the sub is actually traveling eastward at a speed of 37 knots relative to the ocean floor, or the nearest landmass. Just like a crosswind can blow an airplane off course, currents in the water are significant factor that must be calculated when navigating a submarine.

    I assume this:
    is in reference to the shuttle speed. Truth is, this velocity is achieved through sheer brute force. When a rocket is sitting on the launch pad, something like 80-90% of its total weight is just fuel. So, for every one pound of spacecraft that makes it into orbit, eight or nine pounds of high explosive has been blown up underneath the payload to get it up there.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?